The Misuse of RC4 in Microsoft Word and Excel

There’s a nice pdf around that explains how stupid can sometimes programmers or companies be. And that of course affects the(ir) users.
MS supports encryption in word and excel documents (wowZ!) but hey…do they do it “properly” ? Of course not…so people end up believing that they are safe…when in fact they are just wide open to attackers.

Abstract. In this report, we point out a serious security flaw in Microsoft
Word and Excel. The stream cipher RC4 [9] with key length up
to 128 bits is used in MicrosoftWord and Excel to protect the documents.
But when an encrypted document gets modified and saved, the initialization
vector remains the same and thus the same keystream generated
from RC4 is applied to encrypt the different versions of that document.
The consequence is disastrous since a lot of information of the document
could be recovered easily.

This analysis is pretty well written and explains a lot of stuff in a step by step mode. Give your self the chance to find out how you must learn not to trust anyone who provides you “security” and “encryption” services.

Go GO GOOOOOO MS! You did it again!

Looks like RC4 isn’t Microsoft’s favorite algorithm…
Are they SO dumb ? or do they do it on purpose?